Chocoholics receive an SOS

A team of scientists from the University of Amsterdam, with the help of the European Synchrotron Radiation Facility, has taken a major step forward in chocolate science by determining, for the first time, the crystal structure of one of the three main triglycerides that make up cocoa butter. Their results could have mouth-watering results for chocoholics the world over as important clues about how to process this food ingredient are unwrapped.

If you have ever wondered why chocolate sometimes has a white powdery film on its surface, then you are not alone. René Peschar, Henk Schenk and their colleagues in Amsterdam were also puzzled by this white film, known in the food industry as "fat bloom" or sometimes "sugar bloom". Sugar bloom is, as the name suggests, formed as sugar dissolves in surface moisture and then recrystallises. Fat bloom is a slightly slippier problem to handle as it can arise when cocoa butter solids in the chocolate fail to crystallise properly during manufacture or if they undergo a phase shift if stored in warm and humid conditions.

But, unlike other chocoholics Peschar was not satisfied by this simplistic answer. He and his team wanted a more scientific perspective on chocolate blooms. They turned to the ESRF to study the crystal structure of one of the three main triglycerides found in cocoa butter.

It is the crystal form of cocoa butter that determines the physical properties of the chocolate - its texture, its brittleness or otherwise, and the temperature at which it melts. There are a lot of factors to consider in adding cocoa butter and producing a chocolate product because cocoa butter has a high degree of crystallinity and may crystallise in six different polymorphs during production.

"Crystallization is the key step in making chocolate", explains Peschar. "If the crystallization process does not work well then fat bloom occurs, which gives chocolate not only an unattractive look, but makes it less pleasant on the palate."

Manufacturers can control the results by tempering their chocolate, repeatedly heating and cooling it to a specific temperature to produce the thermodynamically second most stable crystal form, which happens to produce the most pleasing texture. The lower phases, I-IV produce poor quality chocolate, while phase VI is almost impossible to achieve. Regardless of the initial cocoa butter phase, however, poor storage can lead to fat bloom.

Peschar and his colleagues focused on the triglyceride, SOS, 1,3-distearoyl-2-oleoylglycerol, a cis-mono-unsaturated fatty acid, which comprises quarter of cocoa butter, and carried out powder diffraction using the ESRF. Knowing the crystal structure of this compound of the cocoa butter phase V, which they also determined, could lead to new approaches to chocolate manufacture that avoid fat bloom.

Dutch machine manufacturing company 'Machinefabriek P.M. Duyvisâ have patented an improved method of making chocolate based on Peschar's work over the last few years and is working with him and a major European chocolate producer on improving the quality of chocolate.

Chocolate blooms have puzzled food scientists for many years.


Chocolate - just too good to resist!